1. Technical Field
The present invention relates to a magnetic detection device for detecting moving direction of a toothed magnetic movable body.
2. Background Art
FIG. 22 shows schematic views of a conventional magnetic detection device according to a prior art, and in which (a) is a front view, (b) is a perspective view and (c) is a partial top view. FIG. 23 is an electric circuit diagram of the conventional magnetic detection device. FIG. 24 is a waveform diagram of the electric circuit diagram shown in FIG. 23. The magnetic detection device is comprised of a rectangular parallelepiped magnet 1 for generating a magnetic field, and an IC chip 2 mounted on the upper surface of the magnet 1 and forming integrally a magneto-resistance effect element 6 serving as a magnetic detection element. Arrow 3 indicates a magnetized direction of the magnet 1. The magnetic detection device is located facing to and bringing close to a toothed magnetic rotor 4. Concave and convex parts of the toothed magnetic rotor 4 comes near alternately the magneto-resistance effect element 6 in the magnetic detection device when the toothed magnetic rotor 4 is rotated. Numeral 5 indicates the rotation axis of the toothed magnetic rotor 4. As a result, a magnetic field applied from the magnet 1 to the magneto-resistance effect element 6 is changed. The change in magnetic field is converted to a change in resistance of the magneto-resistance effect element 6, which is detected in the form of a change in voltage. The change in voltage is output to outside in the form of a pulse wave electric signal of through a comparator in the IC chip and an output transistor. The pulse wave electric signal is transmitted to a computer unit for counting number of pulse waves and detects rotation angle of the toothed magnetic rotor 4.
Generally, the magneto-resistance effect element 6 (hereinafter referred to as MR element) or a giant magneto-resistance effect element (hereinafter referred to as GMR element) is used as the magnetic detection element. The MR element is composed of a thin-film ferromagnetic material (such as Nixe2x80x94Fe, Nixe2x80x94Co, or the like), whose resistance value varies or changes depending on an angle formed between the direction of magnetization and the direction of electric current. The resistance value of the MR element is minimized when the direction of electric current and the direction of magnetization cross at right angles therebetween, and is maximized at 0 degree, i.e., when the mentioned two directions become exactly the same otherwise exactly opposite. The change in resistance value is hereinafter referred to as MR change ratio, which is generally 2 to 3% in Nixe2x80x94Fe and 5 to 6% in Nixe2x80x94Co.
The GMR element is a layered body formed by alternately laminating a magnetic layer and a nonmagnetic layer each being in the range from a few angstrom to a few dozen angstrom in thickness. The GMR element is a so-called super lattice film typically composed of (Fe/Cr), (Permalloy/Cu/Co/Cu) and (Co/Cu). The GMR element performs a MR effect (MR change ratio) remarkably superior to that of the MR element. Furthermore, The GMR element is an in-plane magnetic sensing element for providing the same degree of change in resistance value at all times irrespective of difference in angle between external magnetic field and electric current.
Operation of the GMR element and that of the MR element is substantially the same. Therefore, operation of the MR element is representatively described hereinafter in detail. In FIG. 23, bias magnetic field applied to the MR element 6 is changed by the rotation of the toothed magnetic rotor 4, and resistance value thereof is also changed. In order to detect a change in magnetic field, a bridge circuit 7 is formed using the MR element 6, and a power supply VCC preferably with a constant voltage and current is connected the bridge circuit 7. A change in magnetic field affecting the MR element 6 is detected by converting a change in resistance value of the MR element to a change in electric voltage. This conventional magnetic detection device comprises: the MR element 6; the bridge circuit 7 composed of the resistors 8, 9 and 10; the comparator 13 for outputting a low-level or high-level signal by comparing a voltage at a contact point 11 of this bridge circuit 7 with a reference value 12 of resistors 9 and 10; and an output transistor 14 for receiving an output from the comparator 13 and switching accordingly.
The MR element 6 is connected to the power supply terminal VCC and the resistor 8 is grounded. The contact point 11 between the resistor 8 and the MR element 6 is connected to an inverted input terminal of the comparator 13. An non-inverted input terminal of the comparator 13 is connected to a contact point 12 between the resistors 9 and 10 for generating a reference voltage. The output terminal of the comparator 13 is connected to a base of the output transistor 14 and an emitter thereof is grounded. A collector of the output transistor 14 serving as an output terminal is connected to the power supply terminal VCC in the computer unit 20 through the resistor 15 and is also connected to the inverted input terminal of the comparator 16. The non-inverted input terminal of the comparator 16 is connected to the voltage-dividing circuit of the resistors 18 and 19 for generating a reference voltage (a reference value 17).
FIG. 24 shows waveform diagrams a, b, c, and d each for the corresponding parts a, b, c and d of the circuit diagram shown in FIG. 23 when the toothed magnetic rotor is rotated. When rotating the toothed magnetic rotor 4, a change in bias magnetic field is given to the MR element 6, and an output a corresponding to the concave and convex portions of the toothed magnetic rotor 4 is obtained at the contact point 11 of the bridge circuit 7. This output a is supplied to the comparator 13 where the output is compared with the reference value 12 and is converted to an output b, which is further converted into a binary signal c. This signal c is then formed into a waveform in the computer unit 20 and is then output as a binary signal output d with steep rising and falling transitions. The rotation angle for the toothed magnetic rotor 4 is detected by counting this pulse-shaped output d (not illustrated).
However, in the conventional magnetic detection device of above arrangement, the output c given by the output transistor 14 or the output d given by the computer unit 20 is a binary signal of low or high level in the aspect of signal form. Because signal form of the output remains unchanged irrespective of whether the toothed magnetic rotor 4 is rotated in forward direction or in reverse direction, a problem exists in that it is impossible to detect rotating direction of the toothed magnetic rotor 4.
The present invention was made to resolve the above-discussed problem and has an object of providing a magnetic detection device capable of detecting moving direction of the toothed magnetic movable body.
A magnetic detection device according to the invention comprises: a magnet for generating a bias magnetic field; first and second magneto-resistance effect element units facing to a toothed magnetic movable body to be detected and located in moving direction thereof within the bias magnetic field of the magnet, and of which resistance changes according to change in condition of the bias magnetic field corresponding to movement of the mentioned object to be detected; a first resistance change output circuit for outputting change in resistance of the mentioned first magneto-resistance effect element units; a second resistance change output circuit for outputting change in resistance of the mentioned second magneto-resistance effect element units; and an output signal processing circuit for outputting a first signal according to phase difference between an output of the mentioned first resistance change output circuit and an output of the mentioned second resistance change output circuit based on the movement of the mentioned object to be detected in forward direction, and for outputting a second signal according to phase difference between outputs of the mentioned first and second resistance change output circuits based on the movement of the mentioned object to be detected in reverse direction.
As a result of such arrangement, it becomes possible to detect moving direction of the toothed magnetic moving object using the first signal and the second signal of which values are different from each other.
Another magnetic detection device according to the invention comprises: a magnet for generating a bias magnetic field; first and second magneto-resistance effect element units facing to a toothed magnetic movable body to be detected and located in moving direction thereof within the bias magnetic field of the magnet, and of which resistance changes according to change in condition of the bias magnetic field corresponding to movement of the mentioned object to be detected; a first resistance change output circuit for outputting change in resistance of the mentioned first magneto-resistance effect element units; a second resistance change output circuit for outputting change in resistance of the mentioned second magneto-resistance effect element units; and an output signal processing circuit for outputting a first signal according to phase difference between an output of the mentioned first resistance change output circuit and an output of the mentioned second resistance change output circuit based on the movement of the mentioned object to be detected in forward direction and generating pulses of high level 1 and low level 1 by the mentioned first signal output and the output of the mentioned resistance change output circuit, and for outputting a second signal according to phase difference between outputs of the mentioned first and second resistance change output circuits based on the movement of the mentioned object to be detected in reverse direction and generating pulses of high level 2 and low level 2, which are different from either the mentioned high level 1 or the mentioned low level 1, by the mentioned second signal output and the output of the mentioned resistance change output circuit.
As a result of such arrangement, it becomes possible to detect moving direction of the toothed magnetic movable body using the pulses of high level 1 and low level 1 and using the pulses of high level 2 and low level 2. Furthermore, since the high level 2 and the low level 2 are different from either the high level 1 or the low level 1, at least different three values are provided, eventually resulting in increase in the amount of information available for controlling the system.
A further magnetic detection device according to the invention comprises: a magnet for generating a bias magnetic field; first and second magneto-resistance effect element units facing to a toothed magnetic movable body to be detected and located in moving direction thereof within the bias magnetic field of the magnet, and of which resistance changes according to change in condition of the bias magnetic field corresponding to movement of the mentioned object to be detected; a first resistance change output circuit for outputting change in resistance of the mentioned first magneto-resistance effect element units; a second resistance change output circuit for outputting change in resistance of the mentioned second magneto-resistance effect element units; and an output signal processing circuit for outputting a first signal due to the mentioned first resistance change output circuit of which output is generated earlier than that of the mentioned second resistance change output circuit based on movement of the mentioned object to be detected in forward direction and generating pulses of high level 1 and low level 1 by the mentioned first signal output and the output of the mentioned resistance change output circuit, for outputting a second signal due to the mentioned second resistance change output circuit of which output is generated earlier than that of the mentioned first resistance change output circuit based on the movement of the mentioned object to be detected in reverse direction and generating pulses of high level 2 and low level 2, which are different from either the mentioned high level 1 or the mentioned low level 1, by the mentioned second signal output and the out put of the mentioned resistance change output circuit.
As a result of such arrangement, it becomes possible to detect moving direction of the toothed magnetic movable body using the pulses of high level 1 and low level 1 and using the pulses of high level 2 and low level 2. Furthermore, since the high level 2 and the low level 2 are different from either the high level 1 or the low level 1, at least different three values are provided, eventually resulting in increase in the amount of information available for controlling the system.
It is preferable that the output signal processing circuit includes a D flip-flop circuit. As a result, a circuit of simple arrangement can detect moving direction.
It is preferable that the output signal processing circuit generates pulses by inputting the output from the first resistance change output circuit to an output transistor and a D terminal of a D flip-flop circuit, inputting the output from the second resistance change output circuit to a CL terminal of the mentioned D flip-flop circuit and combining outputs from the mentioned D flip-flop circuit and the mentioned output transistor. As a result, a circuit of simple arrangement can detect moving direction.
It is preferable that the first magneto-resistance effect element unit is a serially connected unit composed of two magneto-resistance effect elements connected in series, and the second magneto-resistance effect element unit is a serially connected unit composed of two magneto-resistance effect elements connected in series. As a result, a detection magnetic device of superior temperature characteristic can be obtained.
It is preferable that one magneto-resistance effect element of the first magneto-resistance effect element unit and one magneto-resistance effect element of the second magneto-resistance effect element unit are located in the center, and the other magneto-resistance effect element of the first magneto-resistance effect element unit and the other magneto-resistance effect element of the second magneto-resistance effect element unit are located on two sides sandwiching the mentioned magneto-resistance effect elements therebetween, in moving direction of the toothed magnetic movable body. As a result, a detection magnetic device of superior temperature characteristic can be obtained.
It is preferable that a GMR element (giant magneto-resistance effect element) is used as the magneto-resistance effect element. As a result, characteristics of the device are improved.